1. Field of the Invention
The present invention relates to a novel photosensitive composition capable of recording a volume type hologram and a volume type hologram recording photosensitive medium produced using the same, and, particularly to a novel photosensitive composition which can be used for graphic arts (GA), security cards, optical elements (HOE) such as color filters, reflecting plates for display, head-up displays or the like and data storage system, and a volume type hologram recording photosensitive medium produced using the same.
2. Description of the Related Art
A system in which as to the three-dimensional information of an object, refractive index modulation is caused inside of a recording layer by an object light (a reflected light from the object) and reference light to record an interference fringe has been known as a volume type hologram. In recent years, a volume type hologram recording photosensitive composition of a dry developing type which does not require wet developing treatment in the production of a volume type hologram and can mass-produce the hologram has attracted considerable attention.
As such a volume type hologram recording photosensitive composition, only an Omnidex series (trademark) available from Du Pont is mass-produced and put on the market. This material uses a radical polymerizable compound, a binder resin, a photo-radical polymerization initiator and a sensitizing dye as its major components and makes use of a difference in refractive index between the radical polymerizable compound and the binder resin. Specifically, when the photosensitive resin composition formed as a film or layer is exposed to interferential light, radical polymerization is initiated at bright regions which are irradiated with more intense light. Along with the polymerization, a gradient of concentration of the radical polymerizable compound is produced, which causes the radical polymerizable compound to diffuse and move from dark regions which are irradiated with weak light to the bright regions. As a consequence, a difference in the concentration of the radical polymerizable compound is caused corresponding to the light intensities of the interference light and appears as a difference in refractive index. This material system has the best performance among volume type hologram photopolymers which have been reported so far and the amount Δn of modulation of the refractive index of this system which amount is calculated based on the Kogelnik theory reaches a maximum of about 0.06. However, the Omnidex series (trademark, available from Du Pont) has the problem that it is weak to heat and is colored and is therefore limited in applications to optical materials.
Also, a material system for a volume type hologram which uses a combination of radical polymerization and cationic polymerization is reported. For example, a system using a compound having a diallylfluorene skeleton as a high-refractive index radical polymerizable compound and a cationic polymerizable compound having a lower refractive index than the radical polymerizable compound is disclosed in JP Patent No. 2873126. In this system, high-refractive index components are polymerized by radical polymerization during hologram exposure and the radical polymerizable compound is diffused and moved to the regions irradiated with light. Then, the image is subjected to fixing exposure to fix it by cationic polymerization, whereby a difference in refractive index is formed according to the distribution of composition and an interference fringe is formed.
Also, a material system for a volume type hologram which utilizes cationic polymerization is disclosed in, for example, U.S. Pat. No. 5,759,721. This material system has the advantage of being free from such oxygen inhibition as seen in a radical polymerization system. However, this system has the problem that it has low photosensitivity to cationic polymerization and also, it is difficult to make this system have sensitivity in a long-wavelength range.
Also, an organic-inorganic hybrid material system for a volume type hologram which uses a combination of an inorganic material network and a photopolymerizable compound is disclosed in JP Patent No. 2953200. This system has the problem that, because an organic polymer is present in a rigid inorganic network, a hologram recording medium is excessively hardened, so that it is difficult to roll it, exhibiting poor processing adaptability and the time required to form a coating layer is made prolonged.
Also, in Japanese Patent Application National Publication No. 2000-508783, a material obtained by dispersing metal ultra-fine particles in a solid matrix is disclosed as a hologram recording material. However, in this material, it is required to make the matrix have fluidity, giving rise to the problem concerning processing adaptability.
Also, a hologram recording material comprising a heat-curable epoxy oligomer, a radical polymerizable aliphatic compound, a photo initiator generating radical species, a photo initiator for activating cationic polymerization and a sensitizing dye is disclosed as a volume type hologram material system having excellent heat resistance in the publication of JP Patent No. 3075081. However, unsatisfactory Δn is obtained in the volume type hologram described in this publication.